Hydrogen storage materials are of interest with respect to devices that employ the reversible gas phase absorption/desorption of hydrogen. Such devices include, but are not limited to, rechargeable batteries, hydrogen storage, pumping and compression systems, and hydrogen storage units, hydrogen absorption refrigerators (or cryocoolers) and other devices that involve the reversible gas phase absorption/desorption of hydrogen.
Certain compounds are candidates for use as hydrogen storage materials. These compounds include, but are not limited to, LaNi.sub.5 and other compounds of the AB.sub.5 type, such as YNi.sub.5, CeNi.sub.5, MmNi.sub.5 where Mm is mischmetal, and MmNi.sub.3.5 Co.sub.0.8 Al.sub.0.4 Mno.sub.0.3 which have a hexagonal Laves phase stucture with advantageous hydrogen storage characteristics. These hydrogen storage materials typically are manufactured by forming a melt of appropriate composition, casting the melt as an ingot, and mechanically crushing the ingot to produce powder having acicular particle configurations for the most part. The cast and crushed powder making technique suffers from numerous disadvantages including chemical inhomogeneity of the crushed powder produced as a result of chemical segregation effects that occurs during ingot solidification. Chemical inhomogeneity of the powders exerts an adverse effect on the hydrogen absorption pressure/temperature response of the material and produces inconsistent hydrogen absorption properties that can limit performance of hydrogen storage components produced from such cast and crushed powders. Therefore, lengthy and energy consuming heat treatments must be performed to homogenize chemical composition across the castings prior to crushing.
Moreover, hydrogen storage components such as electrodes for electrochemical energy storage devices made from the cast and crushed powder can suffer mechanical fracture and component failure due to the extreme volume expansion/contraction cycle that the particulate material experiences (on the order of 25% strain) during hydrogen absorption/desorption cycling of the component in service. For example, LaNi.sub.5 type alloys used as electrodes in nickel/metal hydride (Ni/MeH) battery systems exhibit energy storage capacity reduction and eventual inactivity because fracture of individual particles that form the negative electrode cause internal open circuits which merge to break general contact with the battery electrode. Mechanical fracture of the electrode can result in loss of active material from the electrode and/or electrical shorting as a result of bridging of the fractured electrode with the battery separator.
Avoidance of electrode fracture thus is important to preserve the electrode operating function and battery performance.
The present invention has an object to provide ultrafine hydrogen storage alloy powders, components and method of making same that overcome the aforementioned disadvantages associated with the cast, heat treat, and crush technique for making hydrogen storage powders.